The patient's presentation is consistent with heart failure and echocardiographic findings suggest restrictive cardiomyopathy. Hemochromatosis is the only answer option associated with restrictive cardiomyopathy.
An echocardiogram revealing preserved ejection fraction, impaired diastolic relaxation with biatrial enlargement with increased left ventricular and right ventricular wall thickness with normal chamber size, is evidence of a restrictive cardiomyopathy. Of the answer choices listed, only hemochromatosis is known to cause a restrictive cardiomyopathy. The other options all cause a dilated cardiomyopathy, and would not be distinguishable on echocardiogram.
Restrictive cardiomyopathy results in a decrease in diastolic function due to decreased ventricular compliance and is often associated with myocardial infiltrative disorders, such as hemochromatosis. Other infiltrative causes of restrictive cardiomyopathy include amyloidosis, idiopathic eosinophilia, carcinoid syndrome, sarcoidosis, and glycogen storage disease. Scleroderma and radiation can also result in a restrictive cardiomyopathy.
Wexler et al. review the four major types of cardiomyopathy: dilated cardiomyopathy, hypertrophic cardiomyopathy, restrictive cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy. Treatment of restrictive cardiomyopathy is challenging as most underlying causes usually do not respond to intervention. In the case of hemochromatosis, chelation therapy and phlebotomy may be tried. Additionally, there is no proven treatment for diastolic heart failure and is treated similarly to systolic heart failure.
Felker et al., based on a cohort study of 1,230 patients with cardiomyopathy and a mean follow-up of 4.4 years, concluded that patients with cardiomyopathy due to infiltrative myocardial diseases have worse prognosis that those with other forms of cardiomyopathy.
Image A is an echocardiogram displaying typical findings of restrictive cardiomyopathy: increased left ventricular and right ventricular thickness with normal chamber size and biatrial enlargement.
Illustration A depicts the normal pressure-volume loop in the heart. In a restrictive cardiomyopathy, decreased compliance results in a decrease in the change in volume for any change in pressure within the left ventricle.
Illustration B is an echocardiogram displaying typical findings of dilated cardiomyopathy (dilated ventricles with normal or thin walls).
Answers 1, 3-5: Doxorubicin, alcohol, myocardial infarction, and viral myocarditis all result in a dilated cardiomyopathy, which would typically be associated with reduced systolic function of the left ventricle.
Wexler RK, Elton T, Pleister A, Feldman D. Cardiomyopathy: an overview. Am Fam Physician. 2009 May 1;79(9):778-84. Review. PubMed PMID: 20141097; PubMed Central PMCID: PMC2999879.
PMID:PMC2999879 (Link to Abstract)
Felker GM, Thompson RE, Hare JM, Hruban RH, Clemetson DE, Howard DL, Baughman KL, Kasper EK. Underlying causes and long-term survival in patients with initially unexplained cardiomyopathy. N Engl J Med. 2000 Apr 13;342(15):1077-84. PubMed PMID: 10760308.
PMID:10760308 (Link to Abstract)
USMLE World Step 1 QBank Question #93. Copyright © USMLEWorld, LLC 2012